Research on the neurocognitive consequences of chronic heroin use is sparse, despite the global existence of millions of addicts and young initiates. Most U.S. studies include polydrug abusers and are unable to precisely distinguish between neurocognitive consequences of specific drugs. This deficit is particularly true for heroin addiction, which is often also preceded by several years of extensive use of other drugs, confounding the ability to assess single drug effects. Thus, it is important to determine whether there are neurocognitive impairments associated specifically with heroin addiction that may differ from those associated with alcoholism or whether the same deficits are common to multiple drug users. To elucidate differential neurocognitive consequences of heroin use, it is necessary to identify a population with a dependency on only one drug. Most studies of drug effects on brain function also do not measure prefrontally modulated executive cognitive function (ECF) and focus largely on general neuropsychological function. Recent research using state-of-the-art cognitive instruments provides support for a relationship between specific dimensions of ECF and drug abuse propensity and persistence. ECF may predict relapse propensity, and intact function may be a prerequisite for favorable responses to treatment programs that require a certain level of cognitive processing. There is also insufficient research on gender disparities in the cognitive consequences of drug use, despite differences in historical patterns of use, neurologic drug effects, and involvement of contextual factors. ECF assessment of male and female heroin addicts entering treatment is useful for the evaluation of aspects of cognitive functioning that may be relevant for optimal therapeutic management and treatment planning. To evaluate differential relationships between ECF in heroin addicts versus alcoholics among these groups, the proposed study will focus on single drug users without extensive prior use of other drugs from an inpatient treatment facility in St. Petersburg, Russia. Two control groups will be included: polydrug abusers from the facility and a group of nondrug abusers from the community. Neurocognitive tests will be administered after detoxification. Mediating effects of personality traits on cognitive outcomes will further be assessed. This innovative design and unique sample population will generate findings critical to understanding differences in ECF among heroin addicts, alcoholics, and polydrug abusers, as well as differential gender effects. Because the nature and degree of recovery from drug abuse are likely a function of the type or pattern of neurocognitive impairment, differential drug effects must be considered. This study will significantly contribute to NIDA's goal to support international collaborative research to increase understanding of consequences of drug abuse.